My integra doesn't have cameras but it monitors steering input and the road lines. I turned it off immediately but a family member of mine got frustrated because it would go off on him all the time in his Ford f150.
He often looks for deer while driving and can't drive in a straight line because of it and that drifting to the center line/ edge of the road results in the system telling him to pull over and rest.
I'd assume unless he has a fancy German car he's probably texting while driving or really bad at driving in a straight line. No mass market brand is going to bother installing cameras in the cab unless you are buying fairly expensive luxury car.
Edit: or it's Toyota with their annoying systems. I wouldn't know I avoid cars that scream at you for any little unsafe things it thinks you are doing. Toyota has eye tracking in their new cars and it beeps at you if you look away from the road for a fraction of a second from what I've heard.